direct sunlight discolors the silk and eventually ( in years) will actually break down the product. silk is a protein excreted from a worm.

I dont know how the window coating works but it can't hurt.

They'll most likely deteriorate in as little as one year and while it does help to treat the windows, the pics you're seeing in the books and mags are not only lined, they're also interlined. Silk by itself is very thin and limp and you need to interline to give it that billowy body that you like. Unlined will hang like a limp rag.

If you want something unlined, look at the faux silks, or polyesters. shadylady is exactly right. I can't imagine a silk even hanging nicely if it is unlined. The interlining gives it the lovely soft folds you see. I don't think you'd actually like the look of sun shinning through silk and showing the side hems, etc.

Thanks for your replies. I'm going to line my drapes. Actually the ones that I saw in my book were unlined, but they were a gathered london shade. It did fall very nicely. The fact that light filtered through it gave it a light, airy feel. The captions stated they were unlined. It seems to be the trend now, if you can get away with it.